Louvered screen



Q 4 S p 1967 E. c. STREETER, JR

LOUVERED SCREEN 2 Sheets-Sheet x Filed May 26, 1965 INVENTOR. Edward C Skeeter,

V ATTORNEYS 967 E. c. STREETER, JR

LOUVERED S GREEN 2 Sheets-Sheet 2 Filed May 26, 1965 4 I l l l I.

fer, Jr.

R. vTm? m. an m lw m F C/WQN M M3 v5 2 Fig. 5.

Patented Sept. 19, 1967 3,342,244 LOUVERED SCREEN Edward C. Streeter, Jr., New York, N.Y. (39 Olin St., Ocean Grove, NJ. 07756) Filed May 26, 1965, Ser. No. 458,970 9 Claims. (Cl. 160-107) The present invention particularly relates to dualglazed fenestration having a louvered sun screen positioned in a hermetically sealed space between transparent plates.

The apparent benefits of this shading arrangement have been confirmed in ASHRAE Research Report 1721 entitled, Solar Heat Gains Through Slat-Type Between- Glass Shading Devices, by N. Ozisik and L. F. Shutrum, published in ASHRAE Transactions, volume 66 (1960), pages 359373.

A number of these between-glass shading screens are commercially available. Some have fixed horizontal lou vers, and others are similar to diminutive Venetian blinds. The versatility of the adjustable louver screens is somewhat offset by the need for periodically cleaning the inside surfaces of the glass because the dual-glazed unit must be openable for screen maintenance.

One of the most satisfactory fixed louver screens comprises a plurality of elongated horizontally disposed flat louvers .047 inch wide and .0075 inch thick arranged in vertically spaced relationship, 17 louvers to the inch, and secured together by a series of vertically disposed pairs of fine Wire that are laterally spaced every half inch, looped over the edges of the louvers, and either twisted or welded together between the louvers. The upper surfaces of the louvers are inclined outwardly at an angle of 17 degrees to the horizontal in order to obtain optimum shading without unduly obscuring the view. The unobstructed visibility in a direction parallel to the plane of the louvers is 84 percent of the screen area. This is believed to be the best visibility of any fixed-louver between-glass screen now available.

It is necessary to prevent screens of the above type from buckling, which condition impairs both the appearance and the shading efficiency. Buckling can be avoided by placing the screen in contact with both plates of glass. Some screens are also embedded in plastic. However, this contact destroys the insulating value of the air space. Alternatively, the vertically disposed pairs of wire must be maintained under uniform and relatively great tension of from 9 to 24 pounds per foot of screen width. The screen is secured to one or both glass plates to carry this load, and usually the vertically disposed wires pass through the hermetic seal in order to apply the load to the top and bottom edges of the glass. This expedient jeopardizes the hermetic seal, which is at best precarious, and uses the glass as a load bearing member contrary to the recommendations of the fiat glass industry.

The screen according to the present invention comprises parallel transversely spaced louver assemblies, each assembly including a multiple-Wave extension spring for rendering the assembly longitudinally resilient, and a frame for tensioning the louver assemblies longitudinally. Each louver is preferably made of metallic foil finely corrugated to serve as the extension spring. The corrugations, say 25 waves to the inch, stiffen the louvers transversely, accommodate thermal expansion and contraction of the louvers relative to the frame, and compensate for unavoidable dimensional tolerances. The enclosed location of the louvers protects them from damage; consequently they can be made of extremely thin material. The louvers are advantageously formed from the thinnest foil, for example .001 inch thick, that uniformly maintains substantially the same mechanical properties as thicker sheets of the material. The thinness of the material permits the necessary longitudinal resilience to be obtained with such fine corrugations that the overall or apparent thickness of the louver is still very small, for example .017 inch thick. In fact, the ratio of the apparent thickness of the louver to the louver spacing is far less than that of the above-discussed fiat louver for the same width to spacing ratio. A further result of the thinness of the material is that the sag of the louver can be kept less than an acceptable maximum by a modest longitudinal tension. Accordingly, the tensile load is sufiiciently moderate to be supported by a frame that does not unduly encroach on the viewing area and. neither stresses the glass nor threatens the hermetic seal. Buckling is no problem because eachlouver is individually resiliently supported. The lack of vertical supports in combination with the surprising apparent thinness of the corrugated louvers permits the new screen to have several times less obstruction to vision than the flat louver screen.

The corrugated louvers are very suitable for use in a frictionless adjustable screen wherein each louver is axially tensioned by a torsionally resilient suspension, and a permanent magnet rotor attached to one end of the louver exerts a torque to hold the louver at an angle adjustable in accordance with the strength of a remotely controlled magnetic field. However, louver adjustability is not an essential feature of the present invention, which is therefore disclosed with reference to a fixed louver screen for the sake of simplicity and brevity.

The new screen may be used in a dual-glazed Window unit employing an organic seal where the frame can also serve as the spacer member for the glass plates. On the other hand, the problem of mounting a fixed louver screen in a dual-glazed unit employing a metal-to-glass seal has been particularly troublesome. Accordingly, it is this later environment that has been chosen for the illustrated embodiment of the invention.

In order that the new screen may be described in de tail, reference is now made to the accompanying drawings wherein:

FIG. 1 is an edge view of a corrugated louver,

FIG. 2 is a cross section of the corrugated louver shown n FIG. 1 taken along the dashed line 2-2 in the direction of the arrows,

FIG. 3 is a front elevation the outdoors side,

. FIG. 4 is a horizontal cross section of an enlarged portion of the screen taken along dashed line 4-4 of FIG. 3 in the direction of the arrows, showing details of the louver connection to the screen frame,

FIG. 5 is a front elevation of the lower left corner of a dual-glazed window unit containing the screen viewed from the outdoors side,

FIG. 6 is a horizontal cross section of the portion of the dual-glazed unit shown in FIG. 5 taken along the dashed line 66 in the direction of the arrows, and

FIG. 7 is an elevation of a portion of a beam and a louver attachment strip secured thereto viewed from within the screen frame.

Referring now to FIGS. 1 and 2, a. corrugated louver 11 having a longitudinal axis of symmetry 12 comprises half waves having alternately convex and concave circular cylindrical arcuate surfaces facing the same direction that interconnect on the axis 12. The louver 11 acts under axial tension as a multiple-wave extension spring wherein the thickness t and width b of the material, the overall or apparent thickness 1 of the unstressed louver, and the chord c of the unstressed half waves are known.

of a greatly magnified portion of the screen viewed from the centroidal axis of half wave to the center of curvature of unstressed half wave (in),

r (approximately) where =half angle subtended by are of half wave (radians), and

where s=length of arc of half wave (in.).

The spring characteristics of the louver can now be determined by a method useful with beams of uniform cross section having forces and reactions only at their ends. It can be shown that sx EI where x=extension per half wave from its unstressed chord length (in), F =axial tension (1b.), E=modulus of elasticity (p.s.i.), I =bt /12=area moment of inertia of the rectangular cross section of the half wave relative to its neutral width axis (in/ and l linear moment of inertia of the arc of the half wave relative to the longitudinal axis extending through the chord (in.

The linear moment of inertia I can be expressed in terms of the radius r and the angle of the half wave as 3 sin 5 cos It is observed that I, =r 1r/ 2 when =1r/ 2, that is, when the half waves are semicylindrical, but this shape is not easily produced.

The total extension X of the louver from its unstressed length in response to the axial tension is where n=number of stressed half waves, L=length of the stressed louver, and the other terms have been defined. The louver spring rate F /X is thereby determined.

The sag at the midpoint of an axially horizontal louver caused by its own weight is equal to the maximum deflection of a simple beam under combined axial tension and uniform longitudinal loading. Since the louver is inclined to the horizontal, its weight acts at an angle to the two planes of symmetry of the louver. However, it is clear that the louver has negligible flexural rigidity resisting bending about its width axis. Further it can be shown that the flexural rigidity of the louver resisting bending about its thickness axis is also very small because it is sub stantially nullified by the longitudinal resilience of the louver. Accordingly, the deflection of the corrugated louver is independent of louver angle and the maxi-mum sag Y can be expressed as wL -sr s where w=weight per unit rectilinear length of stressed corrugated louver, and the other terms have been defined.

The weight of the stressed corrugated louver is related to the weight of a flat louver of the same material as follows:

where w =weight per unit length of the flat material, and the other terms have been defined. It is now possible to evaluate the maximum sag and the sag to span ratio of any louver.

The change in louver sag as a function of temperature is now considered. The frame struts that hold apart the beams supporting the louvers have substantially the same thermal co-efiicient of linear expansion as the louvers. However, the struts and louvers will rarely be at the same temperature if there is any flow of heat through the screen. This temperature difference causes a change in the relative lengths resulting in a change in the tension on the louvers. This tensional change is very slight be cause of the compensating effect of the louver resilience. Accordingly, the change in louver sag even with large temperature differences is almost imperceptible.

The maximum stress a on the louver occurs on the concave surface of each half wave at the midpoint furthest from the longitudinal axis 12. This stress is the sum of the stress due to the axial tension and the tensile stress due to the bending moment, and it can be expressed KMd ""A 1., 10

where A=bz=area of the cross section of the material (in. M=Fh moment at the centroidal axis (lb. in.), d=t/2=:distance of the concave surface from the centroidal axis (in), K=half wave curvature correction factor dependent upon the ratio r/d, and the other terms have been defined. The correction factor has the value K=1.078 when r/d=l0, and K:l.037 when r/d=20.

It is now evident that it is advantageous to make the louvers of the thinnest foil practical because the apparent thickness of a louver of given length, width and material and the necessary tension thereon are directly proportional to the material thickness when the corrugation shape is similar and the resilience, sag and stress are constant.

A comparison of a stainless steel louver with an aluminum alloy louver is instructive. A work hardened austenitic stainless steel such as A151 #302 has a relatively high yield strength of 135,000 p.s.i. and a very low secondary creep rate at the operating temperatures. However, the density and also the moduls of elasticity are substantially three times that of the aluminum alloy. Accordingly, for the same length, width, corrugation shape, resilience, sag and apparent thickness, the stainless steel must have the foil thickness and be held at 2.1 times the tension, which subjects it to 4.4 times the unit stress.

The screen must have a very long service life capable of outlasting the hermetic seal and, preferably, not requiring replacement during the estimated life, say 50 years, of the building in which it is installed. The design of the screen, its protected environment, and its service conditions are evidently such that no failure is to be anticipated from wear, temperature and humidity changes, mechanical shock, metal fatigue or corrosion. However, the stressed metal foil of the louvers is subject to a continuous infinitesimal plastic flow or creep, which produces a stress relaxation tending to increase the sag of the louvers until ultimately the sag may exceed an acceptable limit. Fortunately, it is possible to predict by a method now to be discussed the louver sag in the distant future for any assumed louver temperature-time relationship.

The total secondary creep strain or deformation of a metal is a function of the creep stress and a temperaturecompensated time parameter teover a range of temperatures where a single thermally activated deformation process predominates. This function relationship can be expressed as e=f(a ,te (11) where s=total secondary creep strain (in.), a =creep stress (p.s.i.), t=time during secondary creep (hrs), B=metal constant, and T=abso1ute temperature K).

Two identical louvers under the same initial tension will experience substantially the same sag as a result of secondary creep if their temperature-compensated time parameters are equal and if the metal constant B is substantially independent of temperature within the temperature range considered. This relationship can be expressed as Thus a relatively short duration test at a somewhat elevated temperature can provide sag data that can be extrapolated with considerable assurance to a very much longer time at a lower temperature. For example, high purity aluminum has a constant B=13,750' in the temperature range from 250 K. to 375 K. If t=438,000 hours (50 years), T=308 K. (94 F.) and T=373 K. (212 F.), then t=l83 hours (7 /2 days).

Long screen life is achieved by keeping the initial maximum louver stress as small as practical, say A; or A of the yield stress of the material and by preventing the louver temperature from rising excessively above the temperature of the outdoors air. Ordinary glass rather than heat absorbing glass and a louver surface finish having low solar energy absorptance are desirable for this reason. These desiderata are compatible with excellent sun shad- The beams of the frame perform their function of supporting the louvers under conditions of lower temperature and substantially lower stress than those to which the louvers are subjected. Accordingly, the creep of the beams does not limit the life of the screen.

Corrugated louvers are formed from work-hardened foil having a spring temper that permits substantially no further elongation. A very satisfactory method of continuous and rapid corrugation is to pass the fiat foil between the engaging teeth of two spur gears, for example, standard full depth involute teeth with a 72 diametral pitch and a 20 pressure angle. In practice, a web of foil is drawn through parallel circular blades that slit the web into a plurali y of louver-width ribbons before the foil is fed to the corrugating gears. The apparent thickness and resilience of the louvers can be varied considerably by adjusting the depth to which the gears mesh.

A sun screen is shown in FIG. 3 comprising a plurality of corrugated foil louvers 11 supported only at their ends by a rectangular metal frame 13. The louver longitudinal axes 12 are horizontal and equally spaced in a common vertical plane with the upper surfaces of the louvers inclined slightly outwardly at a predetermined angle, say 17, to the horizontal plane.

The frame 13 is formed by a pair of vertical beams 14 and 15 held apart by a pair of horizontal struts 16 and 17. The beams and struts have generally rectangular hollow cross sections. SideslS and 19 of the beams 14 and 15, respectively, face the interior of the frame 13 and are cut away adjacent their ends where the struts 16 and 17 (see FIG. 5) abut the beams. L-shaped corner braces 21 have legs that fit inside the beams and struts to which they are secured by pins 22 to render the frame 13 rigid.

Each end of each louver 11 is provided with a fastener 23 (see FIG. 4) comprising a resilient C-shaped wire hook 24 and a rectangular backing plate 25. The hook 24 is formed with a transverse central portion 26 that nests snugly in a corrugation of the louver spaced one or two corrugations from its end 27. A pair of resilient arms 28 and 29 extend from the hook central portion 26 along either edge of the backing plate 25 generally parallel to the longitudinal axis 12 of the louver 11 and terminate beyond the louver end 27 in fingers 32 and 33, respectively, that project toward each other parallel to the axes of the louver corrugations and substantially coplanar with the backing plate 25.

The backing plate 25 has the same width as the louver and underlies it opposite the hook central portion 26. The hook 24 and the backing plate 25 are held together by weldments 31 that pierce the louver material and act like rivets to clamp the louver 11 to the fastener 23. The backing plate 25 extends beyond the louver end 27 nearly to the hook fingers 32 and 33, thus occupying most of the area enclosed by the hook arms 28 and 29.

Louver attachment strips 34 and 35 are secured to the beam sides 18 and 19, respectively, to connect the louver end fasteners 23 to the beams 14 and 15, respectively. The strips 34 and 35 are mirror images of each other, have a width substantially the. same as the louvers, and extend along the longitudinal centerlines of the beam sides 18 and 19, respectively, between the columns 16 and 17. The strips 34 and 35 lie flat against the beam sides 18 and 19, respectively, except where V-shaped grooves 36 and 37, respectively, cross the strips at the angle to the perpendicular chosen for the louvers 11. The vertical spacing of adjacent grooves is the same as the desired separation of the louvers. The grooves 36 and 37 face the beam sides 18 and 19, respectively, and form recesses that are dimensioned to receive the hook fingers 32 and 33. The resilience of the hook arms 23 and 29 not only permits the fingers 32 and 33, respectively, to clear the ends of the grooves during assembly but keeps the axes 12 of the louvers 11 in the central plane of the frame 13.

The grooves 36 and 37 are conveniently produced by repeated cycles of a punch press, and pilot holes 38 and 39, respectively, are provided to help predetermine the groove spacing. The spacing tolerances lie between Zero and a slight negative value, which permit the elimination of cumulative dimensional errors by slightly stretching the strips 34 and 35 to an overall length that is an exact multiple of the desired louver spacing. The strips yield at the grooves without perceptible distortion.

The strips 34 and 35 are fastened to the beams 14 and 15, respectively, either by screws 41 through pilot holes 38 and 39, respectively, at regular spaced intervals or by welding.

A dual-glazed window unit is shown in FIGS. 5-6 containing the sun screen of FIG. 3. The window unit comprises two glass sheets 42 and 43 fixed in spaced face to face relationship by a lead alloy spacer strip 44, providing a hermetically sealed air space, which accommodates the screen frame 13. The spacer strip 44 is permanently secured to the opposed faces of the glass sheets inwardly of their edges through the intermediary of metallic coatings 45 deposited on and tightly adherent to the marginal portions of the glass sheets and solder joints 46 between the metallic coatings 45 and the spacer strip 44.

A protective aluminum frame 47 covers the edges of the glass sheets 42 and 43 and extends over the exposed faces of the glass sufiiciently to hide the screen frame 13. The space between the strip 44 and the frame 47 is filled with a sealing compound 48.

In assembling the dual-glazed unit, the edges of the spacer strip 44 and the surface of the metallic coatings 45 are provided with a layer of solder. The spacer strip 44 is then held in position and sweat-soldered to the metallic coating 45 on one glass sheet 42 or 43. The screen frame 13 is laid on the second glass sheet, the assembled first sheet and spacer strip are inverted over the screen frame 13, and the second glass sheet is soldered to the strip 45.

The screen frame 13 adds only slightly to the weight of the entire dual-glazed unit, and the screens weight is distributed along the bottom portion of the spacer strip 44. The glass sheets 42 and 43 prevent the hook arms 28 and 29 separating sufficiently to allow either hook finger 32 or 33 to disengage from the attachment strips 34 and 35. Normally no contact exists between the louvers 11 and the glass sheets 42 and 43. The resilience of the louvers enables them to accommodate without damage large deflections of the glass sheets toward the central plane of the frame 13 in response to severe storm conditions or heavy impact.

A louver suitable for use in a dual-glazed unit with a half-inch air space may have the following specifications: t=.0()1", b=%", t,,-=.017", c=.020 and F= /s lb. The louver is formed of aluminum alloy #2024-H18 having 7 a yield strength of 60,000 p.s.i., E=10.2 10 p.s.i., w =3.7 10 lb./in. and a thermal coefiicient of linear expansion C =13 10 in./in./ F. The louvers are inclined at an angle of 17 to the horizontal and are spaced apart a distance a= to provide a louver spacing to louver width ratio a/b=1.25 and a louver apparent thickness to louver spacing ratio t,,/a=.036. From Equations 1, 2, 3 and 4, we have h=.008", r=.01025", =1.35 radians and s .028", respectively. We find I =.91 X in. from Equation 6, permitting x=3.56 10- in. to be determined from Equation 5.

If a louver of the above specifications has a stressed length of 5 feet, then L=60 and Equation 7 gives 11:2,950 half waves and X =1.05"; consequently the spring rate of the louver F/X=.119 lb./in. The maximum sag Y=.182" is found from Equation 8 with the knowledge of w:5.1 10- lb./in. obtained from Equation 9. This results in a sag to span ratio Y/L=1/ 330. The maximum stress r=16,900 p.s.i. is given by Equation 10. The negligible change in louver sag with change in temperature is demonstrated by assuming a difference of 100 F. between the louvers and the frame struts. Under this extreme condition, there is a change in sag AY=.015. Finally, it can be shown that the flexural rigidity of this corrugated louver resisting bending about the longitudinal axis is 438 times greater than the rigidity of a flat louver of the same material, material thickness and width.

I claim:

1. A louvered screen comprising parallel, transversely spaced non-contiguous elongated free-span louvers of corrugated metallic foil, the axis of said corrugations extending parallel to the width of said louvers rendering said louvers longitudinally resilient, and means for tensioning said louvers longitudinally.

2. A louvered screen according to claim 1 wherein the louver material is less than two-thousandths of an inch thick.

3. A louvered screen according to claim 1 wherein the louvers are made of a spring-tempered aluminum alloy.

4. A louvered screen according to claim 1 wherein the ratio of the amplitude of the corrugations of the transverse spacing of the louvers is less than 1/ 20.

5. A louvered screen comprising individual free-span louvers of corrugated metallic foil having horizontal, transversely spaced longitudinal axes, every portion of the louver that has a length equal to the louver width containing a plurality of corrugations, a frame for supporting said louvers under axial tension, and transparent plates parallel to said frame for hermetically sealing said louvers from the ambient atmosphere.

6. A louvered screen comprising a plurality of noncontiguous corrugated metallic foil free-span louvers, and a frame for supporting said louvers in parallel spaced relation by tensioning them along their longitudinal axes, each louver comprising a multiple-Wave extension spring formed of interconnected half waves having alternately convex and concave generally circular cylindrical arcuate.

surfaces with the axes of said coils parallel to the Width axis of the louver.

'7. A sun screen comprising non-contiguous ribbon-like louvers having transversely spaced longitudinal axes, each louver having the shape of substantially uniform interconnected parallel waves, the axes of the Waves being substantially perpendicular to the longitudinal axis of the louver and the amplitudes of the waves being small compared to the transverse spacing of the longitudinal axes of the louvers and a frame for supporting said louvers only adjacent their ends.

8. A sun screen comprising a frame and a plurality of flexible, independently longitudinally resilient, individually free-span louvers supported adjacent their ends by said frame, said louvers having parallel, transversely spaced longitudinal axes describing flat catenary curves, each louver containing corrugations repeated along its length, the amplitude of each corrugation being small relative to the spacing between said louver axes.

9. A sun screen comprising a plurality of non-contiguous elongated louvers having corrugations in the shape of straight, substantially uniform ridges and hollows, each ridge and hollow extending across the width of the louver, said ridges and hollows being repeated along the length of the louver to impart longitudinal resilience thereto, the overall or apparent thickness of each louver, as measured between the tangent to said ridges and the tangent to said hollows, being small relative to the width of the louver, and means for supporting each of said louvers only adjacent its ends, whereby the resilience of the corrugations compensates for independent variation in the length of each louver.

References Cited UNITED STATES PATENTS DAVID J. WILLIAMOWSKY, Primary Examiner.

HARRISON R. MOSELEY, REINALDO P. MA-

CHADO, PETER M. CAUN, Examiners. 

1. A LOUVERED SCREEN COMPRISING PARALLEL, TRANSVERSELY SPACED NON-CONTIGUOUS ELONGATED FREE-SPAN LOUVERS OF CORRUGATED METALLIC FOIL, THE AXIS OF SAID CORRUGATIONS EXTENDING PARALLEL TO THE WIDTH OF SAID LOUVERS RENDERING SAID LOUVERS LONGITUDINALLY RESILIENT, AND MEANS FOR TENSIONING SAID LOUVERS LONGITUDINALLY. 